As a power module of the related art, a power module having a configuration in which a metal plate that forms a conductive pattern layer is laminated on one surface of a ceramic substrate, electronic parts, such as semiconductor chips, are soldered on the conductive pattern layer, a metal plate that becomes a heat dissipation layer is formed on the other surface of the ceramic substrate, and a heat sink is bonded to the heat dissipation layer is known.
In a power module substrate used for the power module, a metal plate is bonded to a surface of a ceramic substrate through brazing. For example, in Patent Document 1, heating is carried out in a state in which a brazing foil is temporarily fixed to a surface of a ceramic substrate through the surface tension of a volatile organic medium, and a conductive pattern layer punched out from a base material is temporarily fixed to the surface of the brazing foil so as to volatilize the volatile organic medium, and the resultant is pressurized in the thickness direction, thereby forming a power module substrate having a metal plate and the ceramic substrate brazed thereto.
Meanwhile, for this kind of power module substrate, there is a demand to have a function of a wiring substrate in addition to a function of an insulating substrate and a function of a heat dissipating substrate in accordance with the recently increasing integration, and therefore multi-layering is being studied.
For example, in the metal and ceramic-bonded substrate (power module substrate) as disclosed in Patent Document 2, a plurality of ceramic substrates having penetration holes as via holes formed therein and aluminum metal plates interposed between the ceramic substrates are provided in a multilayer structure. In this case, the metal plates are formed by feeding and solidifying molten metal between the ceramic substrates that are laminated in a casting mold, and therefore the molten metal is fed and solidified in the penetration holes that are formed in the ceramic substrates so that the metal plates on both sides of the ceramic substrates are electrically connected to each other through the metal in the penetration holes.